Ionizing radiation, such as x-ray and gamma radiation, has been used for years in imaging systems, particularly in medical imaging. Exposure to ionizing radiation has many documented harmful effects, one of the most serious of which is the induction of fatal cancers. All human suspects are susceptible to ionizing radiation in the doses provided by typical imaging technology. However, children are reported to be at approximately ten times greater risk than an average middle-aged adult. This increased susceptibility to the negative effects of ionizing radiation is due in part to the developing and dividing cells of a child's body, which are more susceptible to radiation-induced neoplastic transformation than the cells of an adult. Additionally, children have a greater lifespan remaining than a middle-aged adult for the genotoxic effects of the radiation to manifest.
X-ray radiation, such as that used in a conventional chest x-ray, has been used constructively for a long time to produce medical images. Another type of ionizing radiation imaging technology more recently used is computer tomography (“CT”), typically using x-ray radiation as a source. Conventional x-ray CT technology measures the differential absorption of x-rays passing through the body of an object (or volume) and uses computer analysis of the data by tomographic techniques to produce an image. Conventional x-ray CT technology doses have been found to be similar to the doses that were received by World War II Japanese atomic bomb survivors, a group in whom excess cancer mortality has been observed. Using data from such survivors, Brenner et al. has predicted that the use of conventional x-ray CT technology on infants and children may cause the eventual cancer-related death of 1 out of every 1000 children examined using such CT technology. See Brenner et al., “Estimated risks of radiation-induced fatal cancer from pediatric CT,” AJR Am J Roentgenol. 2001; 176:289–296. This rate is considered by many to be unacceptably high. As an example, of the approximately 12 million infants and children that have been imaged by CT in the United States since the observations by Brenner et al. in 2001, approximately 12,000 are expected to die later in life from cancer initiated by the CT procedure.
Imaging systems that employ ionizing radiation typically include a source for providing the ionizing radiation to an object and a detector for detecting the ionizing radiation that passes through the object. In some cases film serves as the detector. In other cases electronic detectors connected to computer imaging devices are utilized. Adjustments to a source (milliamp, mA and/or kilovolt, kV) can be made to assist in obtaining a desired image exposure. Turning up the total power of the source (and thus the dose of radiation received by the object) can produce a higher resolution image. Turning down the total power of the source (lowering the radiation dose) can produce lower quality images.
Attempts have been made to employ reduced and more judicious use of ionizing radiation imaging with objects prone to increased effect from the radiation doses. Despite this approach with children and infants, the total number of pediatric diagnostic CT images continues to grow each year. Another method used to decrease exposure to ionizing radiation involves adjusting exposure parameters on existing instrumentation to deliver an “as low as reasonably achievable” (ALARA) radiation dose. Exposure parameters include tube current (mA), peak kilovolatage (kVp), pitch, slice thickness, and table speed. Adjustment of exposure parameters is limited by the existing technology (for example, sources and detectors) and can only decrease the total radiation dose to certain levels while still achieving desirable image quality. Further, despite attempts to reduce radiation dose, a wide variability in image scanning techniques still exists that expose many objects to higher than necessary radiation doses. In addition, multi-detector (multi-slice) image scanners are now being used and are inherently more complex, presenting an additional challenge with respect to dose reduction. Systems and methods for further reduction of radiation dose to imaging objects is desired.